JsonDates

Program.cs

using System;
using ServiceStack;
using ServiceStack.Text;

namespace JsonDate
{
    public class Dates
    {
        public DateTime DateOnly { get; set; }
        public DateTime DateWithTime { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var dates = new Dates
            {
                DateOnly = DateTime.Today,
                DateWithTime = DateTime.Now
            };

            using (JsConfig.With(dateHandler: DateHandler.ISO8601DateOnly))
            {
                var json = dates.ToJson(); // {"DateOnly":"2016-03-21","DateWithTime":"2016-03-21"}
            }

            using (JsConfig.With(dateHandler: DateHandler.ISO8601))
            {
                var json = dates.ToJson(); // {"DateOnly":"2016-03-21T00:00:00.0000000+00:00","DateWithTime":"2016-03-21T12:18:58.8551447+00:00"}
            }
            
            // desired json {"DateOnly":"2016-03-21","DateWithTime":"2016-03-21T12:18:58.8551447+00:00"}
        }
    }
}